Imaging technologies-including positron emission tomography (PET)- that are capable of exploiting the power of molecular imaging in small animal models of human disease are a priority in the life-sciences community. In PET, the spatial resolution limit imposed by the range of positrons emitted by F- 18 in tissue is 300-400 micromoles for small detector rings. However, current PET instruments for animal imaging have spatial resolutions on the order of 1.5-2 mm FWHM. Due to the penetrating nature of 511 keV photons and their propensity to scatter within the detector, it is unlikely that present scintillation detector technology can be pushed much below this resolution and achieve adequate performance. This work will develop an alternative detector technology that can easily exploit the resolution limits dictated by the F-18 positron range and acolinearity for small detector ring diameters. Phase I experiments conducted in conjunction with the University of Michigan will demonstrate the feasibility of the detector concept and conduct preliminary design work for PET instruments for imaging mice and rats at sub-millimeter resolution. In Phase II, the design will be finalized, a modular, scalable detector system will be developed, and a prototype instrument containing a partial ring of detectors will be constructed. Phase III will commercialize animal PET instruments based on the technology. PROPOSED COMMERCIAL APPLICATIONS: The immediate application of this technology is in the area of small animal PET. At present, commercial prospects appear good since investigator demand and one manufacturer are creating an emerging market. Although the work proposed herein is for development of animal PET, the basic technology lends itself to improving PET for human subjects as well--an attractive commercial prospect.